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Modal Transient Response

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  • WORKSHOP 4

    Modal Transient Response Analysis

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    MSC.Nastran 102 Exercise Workbook 4-1

    Objectivesn Define time-varying excitation.

    n Produce a MSC.Nastran input file from a dynamic math model, created in Workshop 1.

    n Submit the file for analysis in MSC.Nastran.

    n Compute nodal displacements for desired time domain.

  • 4-2 MSC.Nastran 102 Exercise Workbook

  • WORKSHOP 4 Modal Transient Response Analysis

    MSC.Nastran 102 Exercise Workbook 4-3

    Model Description:Using the Modal Method, determine the transient response of the flatrectangular plate, created in Workshop 1, under time-varying excitation.This example structure shall be excited by a 1 psi pressure load over thetotal surface of the plate varying at 250Hz. In addition, a 25 lb force isapplied at a corner of the tip also varying at 250Hz but starting 0.004seconds after the pressure load begins. Both time-dependent dynamicsloads are applied only for the duration of 0.008 seconds only. Use a modaldamping of = 0.03 for all nodes. Carry out the analysis for 0.04 seconds.Below is a finite element representation of the flat plate. It also containsthe loads and boundary constraints.

    Figure 4.1-Loads and Boundary Conditions

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    12345

    25.0

    12345 12345

    12345 12345 1.0 psi over the total surface

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  • 4-4 MSC.Nastran 102 Exercise Workbook

    Suggested Exercise Stepsn Reference previously created dynamic math model, plate.bdf, by

    using the INCLUDE statement.

    n Specify modal damping as a tabular function of natural frequency (TABDMP1).

    n Define the time-varying pressure loading (PLOAD2, LSEQ and TLOAD2).

    n Define the time-varying tip load (DAREA and TLOAD2). n Define the time delay term in the equations of the dynamic loading

    function (DELAY).n Combine the time-varying loads (DLOAD).n Specify integration time steps (TSTEP).n Prepare the model for a modal transient analysis (SOL 112).n Request response in terms of nodal displacement at grid 11, 33, and

    55.

    n Generate an input file and submit it to the MSC.Nastran solver for normal modes analysis.

    n Review the results, specifically the nodal displacements.

  • WORKSHOP 4 Modal Transient Response Analysis

    MSC.Nastran 102 Exercise Workbook 4-5

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    BEGIN BULK

  • 4-6 MSC.Nastran 102 Exercise Workbook

    1 2 3 4 5 6 7 8 9 10

  • WORKSHOP 4 Modal Transient Response Analysis

    MSC.Nastran 102 Exercise Workbook 4-7

    1 2 3 4 5 6 7 8 9 10

    ENDDATA

  • 4-8 MSC.Nastran 102 Exercise Workbook

    Exercise Procedure:1. Users who are not utilizing MSC.Patran for generating an input file

    should go to Step 11, otherwise, proceed to step 2.

    2. Create a new database and named prob4.db.

    In the New Model Preferences form, set the following:

    3. Create the model by importing an existing MSC.Nastran input file,(plate.bdf).

    4. Activate the entity labels by selecting the Show Labels icon on the tool-bar.

    File/New

    New Database Name prob4OK

    Tolerance u Default

    Analysis code: MSC/NASTRAN

    OK

    u Analysis

    Action: Read Input File

    Object: Model DataMethod: Translate

    Select Input File

    Select Input File plate.bdfOK

    Apply

    OK

    Show Labels

  • WORKSHOP 4 Modal Transient Response Analysis

    MSC.Nastran 102 Exercise Workbook 4-9

    5. Add the pre-defined constraints into a newly defined load case.

    6. Create a time-dependent field for the pressure loading.

    u Load Cases

    Action: Create

    Load Case Name: transient_responseLoad Case Type: Time Dependent

    Assign/Prioritize Loads/BCs

    Select Individual Load/BCs(Select from menu.)

    Displ_spc1.1

    OK

    Apply

    u Fields

    Action: Create

    Object: Non SpatialMethod: Tabular Input

    Field Name: time_dependent_pressureOptions ...

    Maximum Number of t: 21OK

    Input Data ...

    Map Function to Table...

    PCL Expression f(t): sind(360.*250.*t)Start time: 0.0

    End time: 0.008

    Number of Points: 20Apply

    Cancel

  • 4-10 MSC.Nastran 102 Exercise Workbook

    Go back to the Time/Frequency Scalar Table Data window, go down torow 21, and add the following:

    7. Create a time-dependent field for the nodal force.

    Go back to the Time/Frequency Scalar Table Data window, go down torow 32, and add the following:

    Time(t) Value21 0.04 0.0

    OK

    Apply

    u Fields

    Action: Create

    Object: Non SpatialMethod: Tabular Input

    Field Name: time_dependent_forceOptions...

    Maximum Number of t: 32OK

    Input Data...

    Map Function to Table...

    PCL Expression f(t): sind(360.*250.*(t-0.004)) Start time: 0.004

    End time: 0.012

    Number of Points: 31Apply

    Cancel

    Time(t) Value32 0.04 0.0

  • WORKSHOP 4 Modal Transient Response Analysis

    MSC.Nastran 102 Exercise Workbook 4-11

    8. Create the time-dependent pressure.

    9. Create the time-dependent nodal force.

    OK

    Apply

    u Loads/BCs

    Action: Create

    Object: PressureType: Element Uniform

    New Set Name: pressureTarget Element Type: 2D

    Input Data...

    Top Surf Pressure -1* Time/Freq. Dependence(Select from the Time Dependent Fields box.)

    f:time_dependent_pressure

    OK

    Select Application Region ...

    u FEM

    Select 2D Elements or Edge(Click and mouse drag to select all elements.)

    Elm 1:40

    Add

    OK

    Apply

    u Loads/BCs

    Action: Create

    Object: ForceType: Nodal

    New Set Name: force

  • 4-12 MSC.Nastran 102 Exercise Workbook

    To simplify the view, turn off the entity labels using the toolbar.

    In addition, switch to a 3 view isometric view point.

    Under Assigned Load/BC Sets, highlight:

    Displ_spc1.1

    Force_force

    Press_pressure

    Under Select Groups, highlight:

    default_group

    The result should be similar to Figure 4.2.

    Input Data ...

    Force

    * Time/Freq. Dependence(Select from the Time Dependent Fields box.)

    f:time_dependent_force

    OK

    Select Application Region ...

    u FEM

    Select Nodes Node 11Add

    OK

    Apply

    Action: Plot Markers

    Apply

    Hide Labels

    Iso 3 View

  • WORKSHOP 4 Modal Transient Response Analysis

    MSC.Nastran 102 Exercise Workbook 4-13

    Figure 4.2

    10. Generate the input file.

    u Analysis

    Action: Analyze

    Object: Entire ModelMethod: Analysis Deck

    Jobname: prob4Translation Parameters...

    Data Output: XDB and Print

    OK

    Solution Type...

    Solution Type: u TRANSIENT RESPONSE

    Formulation Modal

    Solution Parameters ...

    Mass Calculation Coupled

    Wt.-Mass Conversion .00259

    Eigenvalue Extraction...

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    12345

    25.00

    12345 12345

    12345

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    1.0001.000 1.0001.0001.0001.0001.0001.0001.0001.000

    1.0001.000 1.000 1.0001.0001.000 1.0001.000 1.000 1.000

    1.0001.0001.0001.000 1.0001.00

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